A printed circuit board (PCB) having copper tracks and features when populated with components including capacitors, resistors or active devices (e.g., semiconductor devices including packaged semiconductor devices) electrically interconnected on the board may be referred to as a PCB Assembly (PCBA), or printed circuit assembly (PCA). In a through-hole construction, component leads are inserted in apertures/holes in the board. In a surface-mount construction, the components are placed on pads or lands on the outer surfaces of the PCB. In both of these constructions, component leads are conventionally electrically and mechanically affixed to the PCB with metal solder.
For certain applications (e.g., automotive applications) it is desirable to perform vibration/shock testing of specially prepared test PCBAs to provide board level reliability (BLR) testing which stresses the solder joints between the semiconductor devices and the PCB to obtain reliability data for the solder joints. For a typical test PCBA, there are a plurality of the same packaged semiconductor devices (e.g., ball grid array (BGA) devices, leadframe or quad-flat no-leads (QFN) package) spread over the area of the PCB. The test PCBAs are for BLR testing only and are not configured for use in an end product. Solder joints are generally the weakest link in the interconnection. BLR testing aims to assess solder joint fatigue life or strength. Component level failure mechanisms (e.g. die cracking) can also generally be identified in BLR.
Each semiconductor device and the PCB include metal pads thereon to implement a daisy chain resistor with the solder joints therebetween which provide the electrical coupling between the metal pads on the PCB and metal pads on the semiconductor devices. During testing the test PCBA is mounted into a test fixture that holds the rectangular PCB typically only by its 4 corner/edge positions to provide 4-point support as the test PCBA is vibrated or mechanically shocked to provide mechanical stresses to the solder joints. The daisy chains including solder joints between each of the semiconductor devices on the test PCBA and the PCB are individually monitored electrically (by having their resistance measured) by electrical monitoring equipment to obtain reliability data under the stressed condition(s) for the joints.
Within the last 2 decades, automobile manufacturers have started incorporating electronics in almost every function within the vehicle which has resulted in an increased physical robustness requirement for semiconductor devices. Due to the need to reduce human exposure to hazardous substances (i.e. lead (Pb)), the metal solder used by semiconductor manufacturers for the component leads to be electrically and mechanically fixed to the PCB have reduced the ability to withstand extreme temperature and physical stress such as vibration or mechanical shock.
The National Aeronautics and Space Administration (NASA) performed a vibration experiment in 2007 which confirmed that Pb BGA semiconductor products satisfied their extreme physical requirements, but Pb-free BGA products performed significantly worse when subjected to the same vibration profile. While the semiconductor industry has been responsive to providing automobile manufacturers with increasingly functional devices, there has been little to no updating of the reliability methodologies enlisted to evaluate the physical reliability performance of semiconductor devices on PCBAs.